1. The invention relates to electrophoretic generation of visible images, and more particularly to such generation by means of conductivity patterns and electric fields between electrodes which can be shunted.
2. Description of the Prior Art
U.S. Pat. No. 3,901,696, of which I am a joint inventor and which is assigned to the same assignee, relates to a process and devices for electrophotographic image generation according to a pattern, the details of implementation being incorporated herein by reference, only so much of the description thereof being repeated as is necessary for a proper understanding of the basic elements.
In the referenced process, a photoconductive coating is exposed as a function of a light pattern in order to generate on (or in) the coating a conductivity image which corresponds to the pattern. An electric field, produced with the aid of two electrodes in a space between the photoconductive coating and a member designed to support the image being generated, is controlled by means of the conductivity image. Charged toner particles located in the above-mentioned space are moved by this field, with either the polarity of the toner particle charge and that of one electrode associated with the photoconductive coating being opposite in sign, so that in this first case the toner particles are deposited onto the photoconductive coating, or these polarities being chosen the same in sign, so that in this latter case the toner particles are deposited onto the support. Subsequently, the electric field is collapsed, whereby in the first case, toner particles migrate from the photoconductive coating to the support and generate on it a positive image corresponding to the pattern, and in the second case, toner particles migrate from the support to the photoconductive coating and thus leave behind on the support a negative image corresponding to the pattern.
The referenced patent also discloses a device to implement the above-described process. In the device, the first and second electrodes may be optionally connected to a voltage source or to each other by means of a switch. The device has a photoconductive coating associated with the first electrode, means to image a pattern on the photoconductive coating, a support for the image to be generated, which support is mounted on the second electrode; and means to bring charged toner particles into the space between photoconductive coating and support. Although the process of the reference patent, when compared to the state of the art, permits good color images or chromatic images to be generated, these images may still exhibit an undesirable background. The aim of the present invention is to modify and to improve the referenced process in a manner such that formation of the perturbing background is practically avoided.